The present invention relates generally to extrusion apparatus and, more particularly, to an apparatus for extruding a stream of thermoplastic material through an outlet defined by a pair of flexible lips.
Dies for extruding thermoplastic material typically include a pair of die portions joined together to define an outlet through which molten thermoplastic material is extruded. Specifically, each die portion includes a lip, and the lips of the two die portions cooperate to define a die outlet or lip gap.
In one type of prior art extrusion apparatus, the lips are integral with the die portions and a first one of the lips is joined to a respective die portion by a flexible hinge. Apparatus is provided to adjust the position of the first lip and thus the width of the lip gap. Specifically, the adjustment apparatus includes a plurality of thermally responsive members spaced along the width of the die and a plurality of heater elements each disposed in heat-transfer relationship with a thermally responsive member. The heater elements are individually controlled to adjust the profile of the lip gap at one edge thereof. Alternatively, a manually operable adjustment apparatus may be provided to adjust the width of the lip gap. In either case, the adjustability of the die is limited by the deflection limit of the flexible hinge. Also, the initial set-up procedure to preset the desired outlet width can be undesirably time consuming.
In another prior art extrusion die, referred to as a xe2x80x9csliding lipxe2x80x9d die, first and second die lip members are separate from and carried by respective die portions. The first die lip member is rigidly secured to the die body while a second die lip member is mounted for sliding movement relative to the first die lip member. Again, adjustment apparatus is provided for positioning the second die lip member so that a desired lip gap width is achieved and maintained. While this die design has a wide adjustment range, changing of the gap width can be a lengthy process and gauge control capability is limited.
A third prior art extrusion die includes first and second die body portions, one having a first lip coupled integrally therewith by a flexible hinge and the other having a second, removable lip bolted thereto. A plurality of thermally responsive members is coupled to the first lip for adjusting the position of that lip to achieve a desired extrudate profile. The removable lip, on the other hand, is stationary but can be replaced by other lip members having different dimensions so that the base lip gap can be selected as desired or necessary. This die has relatively good gauge control compared with other prior art die designs but requires a longer time to change the base lip gap and thus has a longer product changeover time.
Because processors of extruded film, sheet, and coatings often must meet their customers"" demands with xe2x80x9cjust-in-timexe2x80x9d deliveries, it is important that the time required to adjust the lip gap dimensions of extrusion dies be kept as short as possible to maximize production of extruded materials and minimize production of scrap material during changeovers. Moreover, because extruded materials are often required in a wide range of thicknesses, it is desirable to provide a single die having a wide adjustment range so that a variety of material thicknesses can be produced without the need to replace the lips or other components of the die and so that minimal reconfiguration time is required.
Yet another die design is disclosed in Ryan et al. U.S. Pat. No. 5,679,383, which is owned by the assignee of the instant application. This die design includes first and second die body portions each having a main body and a lip interconnected with the main body. The die body portions are joined such that a single die outlet is formed between and bounded by the lips, and means are coupled with the die body portions for moving the lips to adjust the die outlet. The moving means includes a lip adjustment block coupled to one of the lips for adjusting the position of the one lip and further includes translating means for translating the lip adjustment block. The translating means includes a sliding angle member having a threaded stud axially extending therefrom and a spool having threads that engage corresponding threads on the stud. Rotation of the spool causes the sliding angle member to be moved in a first direction. The sliding angle member and the lip adjustment block are interconnected by angled flanges or cam surfaces disposed in angled grooves such that the lip adjustment block moves the lip in a second direction transverse to the direction when the sliding angle member is moved in the first direction.
While the die design disclosed in the Ryan et al. ""383 patent has been effective to reduce reconfiguration time, it has been found that problems can be encountered over time. Specifically, the high heat levels developed in the die can cause the grease that lubricates the flanges and grooves to degrade, thereby possibly limiting the adjustability of the device.
In accordance with one aspect of the present invention, an extrusion die includes a pair of die body portions each having a lip wherein one of the lips is moveable toward and away from the other lip about a hinge portion coupled to a main body of one of the die body portions. A pivoting member is coupled to the one lip and a sliding member is engaged with the pivoting member and movable along a first path to cause the pivoting member to pivot and move the lip along a second path transverse to the first path.
Preferably, the die further includes an anchor member having a first end coupled to the sliding member and a second end coupled to the main body wherein the anchor member pivots in response to movement of the sliding member along the first path. Also preferably, the sliding member is channel-shaped with a recess therein and the first end of the anchor member and a first end of the pivoting member are disposed in the recess and coupled to the sliding member at a common point. Still further, the sliding member is coupled to an adjustment member which is movable with the sliding member. The adjustment member preferably includes threads engaged by threads of a rotatable spool and the adjustment member is disposed in an indicator housing secured to the one die body portion. Also, the spool may be restrained against axial movement by a spool retainer secured to the indicator housing and an indicator member may be secured to the adjustment member.
In addition, the spool may be retained at a first end of the die such that rotation of the spool in either of first and second rotational directions causes movement of the sliding member, thereby moving the pivoting member to adjust, in turn, the position of the one lip bidirectionally toward and away from the other lip.
In a specific embodiment, means may be provided for moving the other lip independently of the one lip. Such means may comprise a computer control. The computer control may also be operative to move the sliding member.
In accordance with another aspect of the present invention, an extrusion die comprises a pair of die body portions each having a lip wherein one of the lips is moveable toward and away from the other lip about a hinge portion coupled to a main body of one of the die body portions. A plurality of pivoting link assemblies is coupled to the one lip and a sliding member is engaged with the pivoting link assemblies and movable along a first path to cause the pivoting link assemblies to pivot and move the lip along a second path transverse to the first path.
In accordance with yet another aspect of the present invention, an extrusion die includes a pair of die body portions each having a lip and wherein one of the lips is moveable toward and away from the other lip about a hinge portion coupled to a main body of one of the die body portions. Pivoting links are coupled to the one lip and a channel-shaped sliding member is provided having a recess therein and movable along a first path. A plurality of anchor members is also provided each having a first end coupled to an end of an associated one of the pivoting links and further coupled to the sliding member within the recess, wherein each of the anchor members further has a second end coupled to the one die body portion. A movement apparatus is operable to move the sliding member along the first path and cause the pivoting links to pivot and move the lip along a second path transverse to the first path.